(1) Field of the Invention
The present invention relates to a metal-ceramic composite article and a method of producing the same, and more particularly relates to a metal-ceramic composite article comprising a metal and a ceramic bonded with each other by fitting, and a method of producing the same.
(2) Description of the Prior Art
Ceramics are hard and excellent in wear resistance, and further are excellent in mechanical strength and corrosion resistance at high temperatures. Therefore, ceramics can be used as structural material for a gas turbine rotor and turbocharger rotor, which are required to have high mechanical strength and wear resistance at high temperatures, and it has been investigated to use ceramics in gas turbine rotors and turchocharger rotors. For example, U.S. Pat. No. 4,396,445 discloses a turbine rotor whose blade and shaft are made of ceramics. In the turbine rotor of this structure, a threaded portion is formed at one end of the ceramic shaft, and a metallic impeller of a compressor is fixed thereto. However, the turbine rotor of this structure has a drawback that the threaded portion of the ceramic shaft is broken during the use of the turbine rotor due to the difference of the coefficients of thermal expansion between the metallic material which constitutes the impeller of the compressor, and the ceramic material which constitutes the shaft of the turbine rotor. Moreover, a high precision technique, requiring a long amount of time and a high cost are required for forming threads in the ceramic shaft. In order to overcome these drawbacks, Japanese Utility Model Application Laid-open Specification No. 92,097/82 discloses a turbine rotor having a structure, wherein its ceramic shaft is fitted into a hollow cylindrical portion formed at the end of its metallic shaft. However, this structure has a drawback that, when a ceramic shaft is fitted into a metallic hollow cylinder, whose outer surface has previously been hardened in order to improve the wear resistance of the contacting portion of the metallic shaft surface with a bearing, cracks are formed in the hardened surface portion. Further, when a hardening treatment, such as nitriding or the like, is carried out on the surface of a metallic shaft after the ceramic shaft has been fitted into the metallic shaft, the tightness of the fitted portion is decreased or the ceramic shaft is separated from the metallic shaft. Furthermore, when a ceramic shaft is fitted into a metallic shaft, and then the metallic shaft is subjected to a quenching treatment, the ceramic shaft is separated from the metallic shaft due to the phase transformation of the metallic shaft caused by the quenching. Therefore, in the above described structure, the wear resistance of the contacting portion of the metallic shaft surface with a bearing is poor, and the structure cannot be practically available.